A. Field of the Invention
The present invention relates to a liquid crystal display with a high aperture ratio and method for forming the same. More particularly, the present invention relates to solving disadvantages of crossover shorting and limited viewing angle by using a transparent conductive electrode as a lower electrode of a gate line and a storage capacitor, and depositing anodic oxidative metal on the whole surface of the transparent conductive film after forming a gate electrode, thus making the whole surface of the transparent conductive film anodized. The invention also relates to solving the disadvantage of rubbing in making a liquid crystal display by making the surface of a device uniform, that is, a thin film transistor.
B. Description of the Prior Art
Conventionally, a cathode ray tube (CRT) has been generally used as a display device. However, in recent times, a flat display such as a liquid crystal display (LCD) and a plasma display panel (PDP) have become popular for such use owing to their lightness, thinness and low power-consumption.
An LCD is a non-emissive matrix display, and is classified into a simple matrix-type or an active matrix-type in which a switching element is arrayed in each pixel.
The simple matrix-type of LCD is slower and thus not suitable for application to an up-to-date information processing system in response speed and screen quality. To solve these disadvantages, the active matrix-type LCD has been proposed.
Active matrix-type LCDs are classified into thin film transistor (TFT)-type LCDs and metal insulator metal (MIM)-type LCDs according to the shapes of the switching elements.
The switching element in an TFT active matrix-type LCD includes a field effect transistor having three terminals, including a source electrode terminal connected to a data line, a gate electrode terminal connected to a timing line and a drain electrode terminal connected to an opposite electrode. The operation of turning ON/OFF is operation by a signal from the timing line applied to the gate electrode terminal which carries out the switching operation.
The display characteristic of the LCD is improved by forming a double light shield layer to gain a high contrast and aperture ratio in the formation process of an LCD of the TFT active matrix type. An example of a technique for producing an LCD of the TFT active matrix type using a double light shield layer is suggested in Korean Patent Application Serial No. 91-15530 filed on Sep. 5, 1991 entitled "LIQUID CRYSTAL DISPLAY AND METHOD FOR FORMING THE SAME," which corresponds to U.S. Pat. No. 5,339,181.
The structure of a conventional LCD of the TFT active matrix type is described below with reference to the accompanying drawings:
Referring to FIGS. 1 and 2, a conventional LCD of the TFT active matrix type includes a rear glass substrate 100, a thin film transistor (TFT) gate electrode G arrayed in a matrix on the rear glass substrate 100 and defining a pixel area, a first electrode 10 of a capacitor, an insulating film 2, a semiconductor film 3, a thin film transistor (TFT) source electrode 5b and a thin film transistor (TFT) display signal electrode 5a, a pixel electrode 4, and a storage capacitor C provided in each pixel area.
A margin of the pixel electrode 4 overlaps the first electrode 10 of the capacitor by a predetermined width which is sufficient for producing a border of the margin of each pixel electrode 4. As a result, a disadvantage of a crack in a pixel electrode pattern due to poor coating of the pixel electrode 4 may be overcome.
In addition, overlapping of each TFT source electrode 5b and the entire width of the first electrode of the capacitor may overcome the poor coating of the TFT source electrode 5b along the margin of each pixel electrode 4.
However, the conventional LCDs including the above-mentioned LCD have a disadvantage in that the aperture ratio is 60 percent, which is maximum, and, generally, the aperture ratio is less than 45 percent when opaque metal is employed as the TFT gate electrode material in a pixel of 100 .mu.m.times.300 .mu.m, which is a standard pixel area of 9.4 inches measured conventionally.
The problem of the aperture ratio is more serious in the case of an extended gray array (XGA) of 69 .mu.m.times.207 .mu.m, and it is difficult to obtain an aperture ratio of over 50 percent when the TFT gate electrode is made of the opaque metal.
A low aperture ratio causes an increase of power consumption to obtain the required brightness, as well as a path of light passing through a liquid panel to a predetermined range, thus making the range of viewing angle narrow.